fix(model/paste): interpolate expiration

paste model now consists of expiration instead of lifetime and timestamp.
This is to ensure, that man-in-the-middle attackers cannot derive the origin
of a paste through observing transport layer server request times.

src/httpaste/backend/__init__.py

@@ -26,7 +26,7 @@ class SQLite(Backend):
 
     def __init__(self, parameters: SqliteParameters):
 
-        parameters['connection'] = get_sqlite_connection(parameters)
+        parameters = SqliteParameters(parameters.path, get_sqlite_connection(parameters))
 
         self.user = SqliteUser(parameters, User)
         self.paste = SqlitePaste(parameters, Paste)

src/httpaste/backend/file/paste.py

@@ -7,6 +7,15 @@ from pathlib import Path
 from ast import literal_eval
 
 
+COLUMNS = [
+    'data',
+    'data_hash',
+    'sub',
+    'expiration',
+    'encoding'
+]
+
+
 def load(
         proto: object,
         path: Path,
@@ -22,13 +31,7 @@ def load(
         return None
 
     cells = {}
-    for column in [
-        'data',
-        'data_hash',
-        'sub',
-        'timestamp',
-        'lifetime',
-        'encoding']:
+    for column in COLUMNS:
 
         cell = row.joinpath(column)
 
@@ -56,8 +59,7 @@ def load(
         cells['sub'],
         cells['data'],
         cells['data_hash'],
-        cells['timestamp'],
-        cells['lifetime'],
+        cells['expiration'],
         cells['encoding'])
 
 
@@ -68,13 +70,7 @@ def dump(model: object, path: Path, model_schema: type) -> None:
     row = path.joinpath(model.pid.hex())
     row.mkdir(parents=True, exist_ok=True)
 
-    for column in [
-        'data',
-        'data_hash',
-        'sub',
-        'timestamp',
-        'lifetime',
-            'encoding']:
+    for column in COLUMNS:
 
         cell = row.joinpath(column)
         cell_schema = getattr(model_schema, column)

src/httpaste/backend/sqlite/paste.py

@@ -11,7 +11,7 @@ def load(proto: object, connection: Connection, model_class: type):
     cur = connection.cursor()
 
     cur.execute(
-        'SELECT pid, data, data_hash, sub, timestamp, lifetime, encoding FROM pastes WHERE pid=?',
+        'SELECT pid, data, data_hash, sub, expiration, encoding FROM pastes WHERE pid=?',
         (proto.pid,
          ))
 
@@ -24,8 +24,7 @@ def load(proto: object, connection: Connection, model_class: type):
             result['sub'],
             result['data'],
             result['data_hash'],
-            result['timestamp'],
-            result['lifetime'],
+            result['expiration'],
             result['encoding'])
 
     return None
@@ -38,14 +37,13 @@ def dump(model: object, connection: Connection):
     cur = connection.cursor()
 
     cur.execute(
-        '''INSERT INTO pastes (pid, data, data_hash, sub, timestamp, lifetime, encoding)
-                   VALUES (?,?,?,?,?,?,?)''',
+        '''INSERT INTO pastes (pid, data, data_hash, sub, expiration, encoding)
+                   VALUES (?,?,?,?,?,?)''',
         (model.pid,
          model.data,
          model.data_hash,
          model.sub,
-         model.timestamp,
-         model.lifetime,
+         model.expiration,
          model.encoding))
 
     connection.commit()

src/httpaste/backend/sqlite/paste.sql

@@ -1,10 +1,9 @@
 CREATE TABLE IF NOT EXISTS "pastes" (
-	"id"	BLOB NOT NULL UNIQUE,
+	"pid"	BLOB NOT NULL UNIQUE,
 	"data"	BLOB NOT NULL,
 	"data_hash"	BLOB NOT NULL,
 	"sub"	BLOB UNIQUE,
-	"timestamp"	INTEGER NOT NULL,
-	"lifetime"	INTEGER NOT NULL,
-    "encoding" TEXT
-	PRIMARY KEY("id")
+	"expiration"	INTEGER NOT NULL,
+	"encoding" TEXT,
+	PRIMARY KEY("pid")
 );

src/httpaste/controller/paste/__init__.py

@@ -71,7 +71,7 @@ def get(**kwargs):
                                            config.salt, config.hmac_iterations)
 
     try:
-        data, lifetime, encoding = call()
+        data, expiration, encoding = call()
     except paste_model.LifetimeError as e:
         if kwargs.get('user') is not None:
             paste_model.remove_safe(pid, sub, pkey, config.backend.paste, 
@@ -85,7 +85,7 @@ def get(**kwargs):
         raise ForbiddenError(str(e))
 
     # burn after read
-    if lifetime < 0:
+    if expiration < 0:
         if kwargs.get('user') is not None:
             paste_model.remove_safe(pid, sub, pkey, config.backend.paste, 
                                     config.salt, config.hmac_iterations)

src/httpaste/model/__init__.py

@@ -12,6 +12,7 @@ class PasteDataSchema:
     sub = bytes
     timestamp = int
     lifetime = int
+    expiration = int
     encoding = str
 
 
@@ -54,6 +55,14 @@ class PasteEncoding(PasteDataSchema.encoding):
     """
 
 
+class PasteExpiration(PasteDataSchema.expiration):
+    """Paste Expiration
+
+        < 0: after first acccess
+        0: never
+    """
+
+
 class PasteLifetime(PasteDataSchema.lifetime):
     """Paste Lifetime
     """
@@ -128,8 +137,6 @@ class Paste(NamedTuple):
     #: paste data hash
     data_hash: Optional[PasteHash] = None
     #: paste timestamp
-    timestamp: Optional[PasteTimestamp] = None
-    #: paste lifetime
-    lifetime: Optional[PasteLifetime] = None
+    expiration: Optional[PasteExpiration] = None
     #: paste encoding
     encoding: Optional[PasteEncoding] = None

src/httpaste/model/paste.py

@@ -10,7 +10,7 @@ from httpaste.helper.crypto import dhash, shash, encrypt, decrypt
 from httpaste.helper.common import generate_random_string
 from httpaste.model import (Paste, PasteId, Sub, MasterKey, PasteKey, Salt,
                             PasteData, PasteHash, PasteTimestamp, PasteSub,
-                            PasteLifetime, PasteEncoding)
+                            PasteLifetime, PasteEncoding, PasteExpiration)
 
 
 class NotFoundError(Exception):
@@ -87,8 +87,7 @@ def load(proto: Paste, backend: object) -> Optional[Paste]:
 
         raise SubError('Paste not owned by user')
 
-    if model.lifetime >= 0 and model.timestamp + \
-            (60 * model.lifetime) < int(time.time()):
+    if model.expiration > 0 and model.expiration < int(time.time()):
 
         raise LifetimeError('Paste expired')
 
@@ -121,8 +120,7 @@ def load_safe(
         proto.sub,
         data,
         model.data_hash,
-        model.timestamp,
-        model.lifetime,
+        model.expiration,
         model.encoding)
 
 
@@ -195,6 +193,11 @@ def create(
     sub = None
     timestamp = PasteTimestamp(int(time.time()))
 
+    if lifetime < 0:
+        expiration = -1
+    else:
+        expiration = PasteExpiration(timestamp + (lifetime * 60))
+
     safe_data = PasteData(encrypt(data, pid, salt, hmac_iter))
 
     model = Paste(
@@ -202,8 +205,7 @@ def create(
         sub,
         safe_data,
         data_hash,
-        timestamp,
-        lifetime,
+        expiration,
         encoding)
 
     dump(model, backend)
@@ -234,6 +236,11 @@ def create_safe(data: PasteData,
     safe_sub = PasteSub(shash(sub, data_hash, pid))
     timestamp = PasteTimestamp(int(time.time()))
 
+    if lifetime < 0:
+        expiration = -1
+    else:
+        expiration = PasteExpiration(timestamp + (lifetime * 60))
+
     safe_data = PasteData(encrypt(data, pkey, salt, hmac_iter))
 
     dump(Paste(
@@ -241,8 +248,7 @@ def create_safe(data: PasteData,
         safe_sub,
         safe_data,
         data_hash,
-        timestamp,
-        lifetime,
+        expiration,
         encoding
     ), backend)
 
@@ -279,7 +285,7 @@ def get(pid: PasteId, backend: object, salt: Salt = Config.salt, hmac_iter: int
 
     data = decrypt(model.data, pid, salt, hmac_iter)
 
-    return PasteData(data), model.lifetime, model.encoding
+    return PasteData(data), model.expiration, model.encoding
 
 
 def get_safe(